Method and apparatus for detecting wire fault and electrical imbalance for power over communications cabling

ABSTRACT

In one embodiment, a method includes transmitting Power over Ethernet (PoE) in a PoE distribution system at a power greater than 100 watts, the distribution system comprising at least two pairs of wires, monitoring a thermal condition in the distribution system, periodically checking each of the wires for a fault, and checking for an electrical imbalance at the wires. An apparatus is also disclosed herein.

STATEMENT OF RELATED APPLICATION

The present application claims priority from U.S. ProvisionalApplication No. 62/653,385, entitled WIRE FAULT AND PAIR UNBALANCEDETECTION FOR POWER OVER COMMUNICATIONS CABLING, filed on Apr. 5, 2018.The contents of this provisional application are incorporated herein byreference in its entirety.

TECHNICAL FIELD

The present disclosure relates generally to communications networks, andmore particularly, to safety features for power over communicationssystems.

BACKGROUND

Power over Ethernet (PoE) is a technology for providing electrical powerover a wired telecommunications network from power sourcing equipment(PSE) to a powered device (PD) over a link section. In conventional PoEsystems that use 100 W or less power sources, significant protectionmechanisms are not needed because the limited power systemclassification does not cause destructive damage or life safetyconcerns. In newer systems that may exceed the 100 W threshold, it isimportant to define safety protocol mechanisms that protect both thesystem and the user.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates an example of a system in which embodiments describedherein may be implemented.

FIG. 2 is a front view of a dual route processor card chassis.

FIG. 3 is a top view of the chassis shown in FIG. 2.

FIG. 4 illustrates a dual route processor chassis with an extended powershelf.

FIG. 5A is a front view of a line card chassis.

FIG. 5B is a front view of a dual line card chassis.

FIG. 5C is a front view of a dual fabric chassis.

FIG. 6 is a flowchart illustrating a process for wire fault andelectrical imbalance detection, in accordance with one embodiment.

FIG. 7 is a block diagram of an electrical imbalance detection circuitfor a power source, in accordance with one embodiment.

FIG. 8 is a block diagram of an electrical imbalance detection circuitfor a powered device, in accordance with one embodiment.

FIG. 9 illustrates a wire verification process, in accordance with oneembodiment.

FIG. 10 depicts an example of a network device useful in implementingembodiments described herein.

Corresponding reference characters indicate corresponding partsthroughout the several views of the drawings.

DESCRIPTION OF EXAMPLE EMBODIMENTS

Overview

In one embodiment, a method generally comprises transmitting Power overEthernet (PoE) in a PoE distribution system at a power greater than 100watts, the distribution system comprising at least two pairs of wires,monitoring a thermal condition in the distribution system, periodicallychecking each of the wires for a fault, and checking for an electricalimbalance at the wires.

In another embodiment, an apparatus generally comprises a routeprocessor operable as a power source in a Power over Ethernet (PoE)distribution system, the route processor comprising, a plurality ofports for delivering power to a plurality of powered devices, and afault detection module for monitoring a thermal condition in thedistribution system, checking wires at each of the ports for a fault,and checking for an electrical imbalance at the wires.

In yet another embodiment, a modular transport system generallycomprises a route processor comprising a plurality of ports fordelivering Power over Ethernet (PoE) at a power greater than 100 watts,a plurality of powered devices comprising a plurality of ports forreceiving the PoE, and a fault detection system for monitoring a thermalcondition in the distribution system, checking wires at each of theports for a fault, and checking for an electrical imbalance at thewires.

Further understanding of the features and advantages of the embodimentsdescribed herein may be realized by reference to the remaining portionsof the specification and the attached drawings.

EXAMPLE EMBODIMENTS

The following description is presented to enable one of ordinary skillin the art to make and use the embodiments. Descriptions of specificembodiments and applications are provided only as examples, and variousmodifications will be readily apparent to those skilled in the art. Thegeneral principles described herein may be applied to other applicationswithout departing from the scope of the embodiments. Thus, theembodiments are not to be limited to those shown, but are to be accordedthe widest scope consistent with the principles and features describedherein. For purpose of clarity, details relating to technical materialthat is known in the technical fields related to the embodiments havenot been described in detail.

The maximum power delivery capacity of standard Power over Ethernet(PoE) is approximately 100 watts (W), but many classes of powereddevices would benefit from power delivery of greater than 100 W. For PoEapplications exceeding 100 W, there is a need for safety mechanisms toprotect users and property.

The embodiments described herein provide safety systems and methods thatallow for delivery of higher wattage power over communications cablingto safely deliver power exceeding 100 W for higher ampacity applicationsbeyond conventional 90 W PoE implementations. The safety system may, forexample, prevent unwanted electrical events such as shorts, opens,electrical imbalance, exceeding ampacity limits, or life safetyconcerns. In one example, the system may allow for a safe implementationof up to 300 watts of power delivered over a four-pair communicationscable. The system may, for example, deliver 100 W-300 W power at a cabledistance up to 15 meters. As described in detail below, the embodimentsmay be implemented in a transport router with a RP (Route Processor)control plane in a separate system from line card optics. Both power anddata are passed from the RP device to the line card device in a PSE(Power Sourcing Equipment) to PD (Powered Device) application.

Referring now to the drawings, and first to FIG. 1, an example of amodular transport system that may utilize power over communicationscabling (also referred to herein as enhanced PoE) for powerdistribution. The modular transport system shown in FIG. 1 includes adual route processor (RP) card chassis 10 supplying control and power tothree line card chassis 12. The dual RP card chassis may be, forexample, a 2 RU (rack unit) chassis. The route processor card chassis 10comprises two route processors 14 (RP0, RP1), each comprising twentydownlink ports 16, a dual port ground system 18, and two combinationpower supply unit (PSU) and fan tray modules 20 (PSU/FT0, PSU/FT1). Thescalable transport system may support, for example, up to twentyredundant line card connections or eighteen line card connections andtwo fabric connections. Each downlink port 16 may support, for example,integrated 1 Gb/s or 10 Gb/s with a 300 W power system. The downlinkports 16 supply control and power to each line card chassis 12 (orfabric chassis). In one example, the power supply units 20 provide dual2 kW AC or DC (or other power level) redundant power modules (1+1). Eachline card chassis 12 comprises a line card 22 (LC0, LC1, LC2) comprisingdual uplink ports 24, fan tray 26 (FT0, FT1, FT2), and a ground system28. Power and data are transmitted from ports 16 at the route processors14 to the ports 24 at the line cards 22 via cables 17. In this example,the route processor 14 is the PSE (Power Sourcing Equipment) and theline cards 22 are the PDs (Powered Devices) in the PoE distributionsystem.

In one embodiment, the ports 16, 24 comprise interconnect ports thatcombine data and PoE utilizing an RJ45 (or similar connector). Forexample, the cable and connector system may comprise RJ45 cat7 style, 4pair communications cabling. The ports 16, 24 may be labeled to identifycapability for power over 90 W. In one example, the cable and connectorsystem may support ampacity per pin or wire to 2000 ma, minimum. Forexample, 22 AWG (American Wire Gauge) wire may be used to support 1500ma-2000 ma per wire in a cat7/cat5e cable system. In one example, thesystem may support a cable length of up to 15 meters (based ontechnology of cat7 cable, 22 AWG at 300 W). In one or more embodiments,the internal PSE power supply voltage may operate in the 56V to 57Vrange, 57V to 58V range, or 56V to 58V range. For example, the outputvoltage at the PSE may be 57V with an input voltage at the PD of 56V.For a 15 meter cable, a 56V power supply at the PSE can deliverapproximately 300 W power. With less current, the system may alsodeliver power less than 300 W to lengths beyond 15 meters, for example.

It is to be understood that the arrangement shown in FIG. 1 is only anexample, and other arrangements (e.g., number of route processors, PSUs,line cards, or uplinks/downlinks) may be used without departing from thescope of the embodiments. Furthermore, the connectors, cables, cablelengths, and power ranges described herein are only examples and thatother types of connectors, length of cables, type of cable systems, orpower levels may be used without departing from the scope of theembodiments.

FIG. 2 shows the dual RP card chassis 10 without the line cardconnections shown in FIG. 1, and FIG. 3 is a top view of the dual routeprocessor card chassis shown in FIG. 2. The route processors 14 arecontained within a route processor (RP) slot 30 (FIG. 3). Power supplyunits 32 are positioned in front of fans 34. A plenum space 35 isinterposed between the combined power and fan modules and the RP slot30. Routing of power is shown at 36 and air passages are depicted at 38.

FIG. 4 illustrates a front view of a dual route processor chassis 40 andan extended power system (shelf) 42. The extended power system 42 may beused, for example, to supply four 2 kW redundant power modules (2+2)(e.g., double the delivered power capacity of the RP chassis 10 shown inFIG. 1). The RP chassis 40 includes route processors 43 (RP0, RP1),ground system 44, and combined PEM (Power Entry Module) and fan tray 45(PEM A/FT0, PEM B/FT1. In this example, the extended power shelf 42includes four combined power supply units and fan trays 46 (PSU/FT0,PSU/FT1, PSU/FT2, PSU/FT3) and ground system 48. Power is supplied tothe route processors 43 via two power outputs 47 (power OUT A, power OUTB). The route processor card chassis 40 receives power at the PEMs 45and delivers power at downlink ports (not shown) as previously describedwith respect to FIG. 1.

FIGS. 5A, 5B, and 5C illustrate a line card chassis 50, dual line cardchassis 52, and dual fabric card chassis 54, respectively. Each linecard (LC0, LC1) 55 and fabric card (FC0, FC1) 56 may support, forexample, dual uplink ports 53 with 300 W power. Each line card 55 andfabric card 56 has a corresponding fan tray (FT0, FT1) 57 and eachchassis 50, 52, 54 includes a ground 58. The dual fabric chassis 54 maysupport multiple line card chassis.

It is to be understood that the components and arrangements shown inFIGS. 1, 2, 3, 4, 5A, 5B, and 5C are only examples of modular transportsystems that may utilize the safety systems described herein for powerover communications cable systems.

As previously described, higher power PoE distribution systems (e.g.,≥100 W PoE) present a need for additional fault detection to safelyprotect equipment and users. The following describes a fault detectionsystem and method that may be implemented on the modular transportsystems described above with respect to FIGS. 1-5C or other transportsystems configured for power over communications cabling (e.g., PoEabove 100 W, between 100 W and 300 W, approximately 300 W). The faultdetection (safety) system and method described herein may be used, forexample, to prevent thermal buildup on a multi-pair cable system,wire-to-wire imbalance across a pair of wires, pair-to-pair imbalance,short circuit, or any combination thereof. As described below, thermalbuildup may be detected by monitoring the current in a wire andcalculating a change in temperature for a wire, wire pair, cable (e.g.,four-pair cable) based on known wire parameters. A wire-to-wireimbalance may be detected across a pair if one of the two wires in apair carries substantially more current than the other. A pair-to-pairimbalance may be detected if one of the pairs carries substantially morecurrent than the other pairs. Each wire may also be evaluated toidentify a short circuit or fault. An error or a minor or major alarmmay be generated if a fault is detected. Depending on the severity ofthe detected fault, the power may be reduced or the port may beshutdown. For example, if the thermal buildup is minor, power may bereduced to reduce current on the line. If a short or other fault isdetected on the wire or an electrical imbalance is detected, thecorresponding port may be shutdown.

FIG. 6 is a flowchart illustrating an overview of a process fordetecting faults in the power over communications cabling system, inaccordance with one embodiment. At step 60, the system starts up in alow power mode (e.g., ≤90 W or other low power setting) using, forexample, IEEE standard 802.3bt for Power over Ethernet (e.g., class 8).A channel verification algorithm may be performed to evaluate linksbefore applying power (step 62). For example, a monitoring process mayroll through the wires to verify wire connectivity. The system may thenuse CDP (Cisco Discovery Protocol) (or any other suitable protocol) tonegotiate for power above 90 W, in a similar manner that UPoE (UniversalPower over Ethernet) negotiates up to 60 W from a 15 W or 30 W start(step 63). In one example, the PSE may inform the PD of a power levelthat the PSE is capable of providing and the PD may then select theappropriate power level to use. The PSE and PD may negotiate powerlevels, for example, of 15 W, 30 W, 60 W, 90 W, 150 W, 200 W, 250 W, 300W, or any other suitable power level. If no faults are detected, thesystem may auto negotiate to maximum available power. Ethernetmanagement packets may be used to enable allocation to 300 W maximumpower, for example.

Once the power is increased, fault detection is performed, as describedin detail below. Fault detection may include for example, a check forthermal buildup (step 64), electrical imbalance check (wire-to-wireimbalance check (step 65), pair-to-pair imbalance check (step 66)), orshort circuit/fault protection check (step 67). The system may beconfigured to perform one or more of these checks in any order (asindicated in one example by dashed lines between steps in FIG. 6) orsome steps may be performed simultaneously. One or more of the safetychecks may be performed continuously or at specified intervals. Forexample, the wires may be monitored one by one in a continuous loopwithin a 10 ms window. If a fault is detected or a specified PSE voltage(e.g., 58.5V) is exceeded, power output is shutdown (steps 68 and 69).If the fault is minor (e.g., one or more parameters close to limit butnot exceeding limit), power may be reduced through renegotiation of thepower level. If the fault continues, the port may then be shutdown. Analarm may also be generated. In one or more embodiments, packet and idle(link) monitoring may be used to shut down the power. If a wire is lost,the link is lost and per wire faults are covered.

It is to be understood that the process shown in FIG. 6 and describedabove is only an example and that steps may combined, added, removed, ormodified, without departing from the scope of the embodiments.

The following describes details of safety checks (fault detection) thatmay be performed for steps 64-67 of FIG. 6.

In one or more embodiments, thermal buildup may be detected by trackingcable current change and calculating cable current temperature. Thecable temperature is a function of amperage, cable gauge, and length ofcable. By using known parameters and assuming a wire size (e.g., 22AWG), the temperature limit of the cable in a bundle environment may becalculated. Temperature ranges may be defined, for example, as normal,minor, major, and critical (e.g., minor defined within 20 C.° of cabletemperature limit, major defined within 10 C.° of cable temperaturelimit, and critical defined at cable temperature limit). If thetemperature range is in the minor range, the system may forcerenegotiation of power to reduce current on the line. If the temperatureis in the critical range, the port may be de-energized. The temperaturemay be calculated in each wire, each pair of wires, the four-pair cable,or any combination. Thermal modeling of the cable may be performed asdescribed in U.S. patent application Ser. No. 15/604,344, entitled“Thermal Modeling for Cables Transmitting Data and Power”, filed May 24,2017, for use in fault detection, for example.

Action may also be taken based on the monitored (or calculated) current.For example, if the current in the cable exceeds the cable currentmaximum limit, the port may be shutdown. If the cable current reaches aspecified range, the line card (PD) may be forced to perform powernegotiation with the PSE to reduce current on the line. The current maybe monitored per wire, per pair of wires, per cable, or any combination.Current ranges may be defined as normal, minor, major, and critical(e.g., minor defined within 20% maximum current, major defined within10% maximum current, and critical defined at maximum current). If therange is minor, renegotiation may be performed to reduce current on thecable. If the critical current is reached, the port may be de-energized.

As shown in steps 65 and 66 of FIG. 6, a fault may be identified basedon electrical imbalance. Wire-to-wire imbalance (between wires within apair of wires) and pair-to-pair imbalance (between pairs of wires) maybe tracked. An alarm may be generated if wire-to-wire or pair-to-pairimbalance exceeds a specified limit. Cable degradation may also betracked and a minor alarm generated upon detection of a wire-to-wire orpair-to-pair imbalance. An example of a pair-to-pair imbalance detectioncircuit is shown in FIG. 7 for a PSE and FIG. 8 for a PD and describedbelow.

In one or more embodiments, a fault detection circuit provides per pairfault and imbalance detection in a four-pair communications cable (e.g.,cable comprising at least two pairs of wires). The fault detectioncircuit individually monitors and looks for current disparity, examineslive load to negotiated load, and considers automatic load levelingacross wires for impedance changes. Per wire faults may be detectedusing a center tap and link monitor.

FIG. 7 illustrates an example of a fault detection circuit for per pairfault and imbalance detection at a PoE source, in accordance with oneembodiment. The fault detection is performed for each port (e.g., port16 at route processor 14 in FIG. 1) at the PSE source. Forsimplification the circuit is shown for one of the four-pairs of wiresat one of the ports. A circuit is provided for fault detection for eachpair of wires. The circuit shown in FIG. 7 is located at the PSE (routeprocessor 14 in FIG. 1) and provides a check from a power source 70 to aconnector 71 at the port. The source 70 may provide, for example, 58VDC, or other suitable power level, as previously described. Theconnector 71 may comprise, for example, an RJ45 connector for providingpower and data over a cable to the powered device (e.g., line card 22 inFIG. 1).

A microcontroller 72 (e.g., PIC (Programmable Interface Controller)) maybe used to compare all four pairs and provide an indication of an out ofbalance condition or fault and initiate an alarm. The power passes fromthe source 70 through resistor 73, which is in communication with adifferential amplifier 74. The circuit includes a field effecttransistor (FET) 75 receiving input from the source 70 (via the resistor73) and the controller 72, and providing input to a transformer 76comprising a pair of inductors 77. Power is transmitted to the connector71 from the transformer 76. The controller 72 also receives input from arise and fall detector 78 tapped into Ethernet lines. Ethernet data andcontrol logic is provided by module 79. The Ethernet circuit includesEthernet magnetics 83 and DC blocks 84.

In order to avoid the use of large magnetics to handle both data andpower, the system may use passive coupling instead of integratedmagnetics for data transfer. The system uses AC coupling instead ofpassing through the Ethernet magnetics 79. This avoids the use of largemagnetics to handle both data and power. Capacitors may be used to blockthe DC power from the Ethernet magnetics to prevent a short. In oneexample, capacitors are used inline and inductors are used to deliverpower with matched power inductors.

FIG. 8 illustrates an example of a circuit for per pair fault andimbalance detection at a powered device 80 (e.g., line card 22 in FIG.1), in accordance with one embodiment. As described above with respectto FIG. 7, the circuit is shown for only one of the four pairs forsimplification. The powered device 80 receives power and data from thePSE through the connector 81 (e.g., RJ45 connector). Power istransmitted through inductors 87 and passes through field effecttransistors (FETs) 85. A controller 82 (optional) compares the fourpairs to check for an imbalance between pairs. The circuit in FIG. 8 mayalso be configured without intelligence (e.g., with controller 82removed). In this case, error control is provided directly to the FETs85 from the PD 80 (instead of to the controller). The Ethernet portionof the circuit includes Ethernet magnets 89 and DC blocks 88, aspreviously described.

As previously noted, the system may also check the wires for shortcircuit and provide fault protection for life safety by analyzing eachwire in the cable system within a time period of 10 ms, which is knownnot to interfere with human health. In one embodiment, the system uses acontrol loop to evaluate wire stability at a periodic interval (e.g., 9ms, 10 ms). In one example, a safety algorithm loops within a 10 mswindow. Each wire is monitored for line abnormalities such as shorts andopens at the PSE. Voltage is measured and if there is no error, the loopis repeated. All wires are powered and at time n a first wire (n) isde-energized. In one example, the system cuts power on wire 1 for 0.25ms or less and evaluates power to zero time. The system may wait 1.00ms, for example (wait time contributes to keep average current higherwithout burst), and then loops to the next wire. Fall time is monitoredand calculated based on wire gauge modeled to wire lengthmaximum/minimum range. The wire may also be driven negative to force ashorter monitor time. At time (n) +0.25 ms, a next wire is energized.Rise time is monitored and calculated to wire gauge modeled to wirelength maximum/minimum range. This process continues until all wires arechecked. In this example, the total process takes 10 ms.

FIG. 9 illustrates another example, in which each wire is tested after a1 ms delay. Wire 1 is turned off for 0.25 ms followed by a 0.75 ms delayto evaluate power drop. This process is repeated for all eight wires,resulting in a 9 ms cycle.

The safety algorithm described above may introduce a repetitivefrequency base that may result in both low frequency radiated emissionsand high range conducted emissions. The following algorithms may bedeployed to make the safety mechanism more randomly distributed andavoid this repetitive frequency base.

In order to eliminate EMC (electromagnetic compatibility) spectralpeaking, the algorithm varies the wire_x time span shown in FIG. 9 as0.25 ms+0.75 ms=1.00 ms. Two random numbers may be generated; one numberselects the wire_x to target (integer 1-8) and the other number selectsthe delay time to the next wire_x (0.1 ms-0.75 ms). This results in eachoff time location being distributed across the 9 ms window, as definedwithin the standard 10 ms safety evaluation time window.

It is to be understood that the above described process and timeintervals used in the fault detection process are only examples and thatthe process may include different time intervals or algorithms, withoutdeparting from the scope of the embodiments.

The embodiments operate in the context of a data communications networkincluding multiple network devices. The network may include any numberof network devices in communication via any number of nodes (e.g.,routers, switches, gateways, controllers, access points, or othernetwork devices), which facilitate passage of data within the network.The network devices may communicate over or be in communication with oneor more networks (e.g., local area network (LAN), metropolitan areanetwork (MAN), wide area network (WAN), virtual private network (VPN)(e.g., Ethernet virtual private network (EVPN), layer 2 virtual privatenetwork (L2VPN)), virtual local area network (VLAN), wireless network,enterprise network, corporate network, data center, Internet of Things(IoT), Internet, intranet, or any other network).

FIG. 10 illustrates an example of a network device 100 (e.g., transportsystem, route processor card chassis in FIG. 1) that may be used toimplement the embodiments described herein. In one embodiment, thenetwork device 100 is a programmable machine that may be implemented inhardware, software, or any combination thereof. The network device 100includes one or more processors 102, memory 104, interface 106, and wirefault and pair imbalance detection module 108.

Memory 104 may be a volatile memory or non-volatile storage, whichstores various applications, operating systems, modules, and data forexecution and use by the processor 102. For example, components of thewire fault and imbalance detection module 108 (e.g., code, logic, orfirmware, etc.) may be stored in the memory 104. The network device 100may include any number of memory components.

The network device 100 may include any number of processors 102 (e.g.,single or multi-processor computing device or system), which maycommunicate with a forwarding engine or packet forwarder operable toprocess a packet or packet header. The processor 102 may receiveinstructions from a software application or module, which causes theprocessor to perform functions of one or more embodiments describedherein.

Logic may be encoded in one or more tangible media for execution by theprocessor 102. For example, the processor 102 may execute codes storedin a computer-readable medium such as memory 104. The computer-readablemedium may be, for example, electronic (e.g., RAM (random accessmemory), ROM (read-only memory), EPROM (erasable programmable read-onlymemory)), magnetic, optical (e.g., CD, DVD), electromagnetic,semiconductor technology, or any other suitable medium. In one example,the computer-readable medium comprises a non-transitorycomputer-readable medium. Logic may be used to perform one or morefunctions described above with respect to the flowchart of FIG. 6 orother functions such as power level negotiations or safety subsystemsdescribed herein. The network device 100 may include any number ofprocessors 102.

The interface 106 may comprise any number of interfaces or networkinterfaces (line cards, ports, connectors) for receiving data or power,or transmitting data or power to other devices. The network interfacemay be configured to transmit or receive data using a variety ofdifferent communications protocols and may include mechanical,electrical, and signaling circuitry for communicating data over physicallinks coupled to the network or wireless interfaces. For example, linecards may include port processors and port processor controllers. Theinterface 106 may be configured for PoE, enhanced PoE, PoE+, UPoE, orsimilar operation.

The wire fault and imbalance detection module 108 may comprise hardwareor software for use in fault detection described herein.

It is to be understood that the network device 100 shown in FIG. 10 anddescribed above is only an example and that different configurations ofnetwork devices may be used. For example, the network device 100 mayfurther include any suitable combination of hardware, software,algorithms, processors, devices, components, or elements operable tofacilitate the capabilities described herein.

Although the method and apparatus have been described in accordance withthe embodiments shown, one of ordinary skill in the art will readilyrecognize that there could be variations made to the embodiments withoutdeparting from the scope of the invention. Accordingly, it is intendedthat all matter contained in the above description and shown in theaccompanying drawings shall be interpreted as illustrative and not in alimiting sense.

What is claimed is:
 1. A method comprising: transmitting Power overEthernet (PoE) in a PoE distribution system at a power greater than 100watts, the distribution system comprising at least two pairs of wires;monitoring a thermal condition in the distribution system; periodicallychecking each of the wires for a fault; and checking for an electricalimbalance at the wires.
 2. The method of claim 1 wherein checking for anelectrical imbalance comprises checking for an electrical imbalancebetween said pairs of wires.
 3. The method of claim 1 wherein checkingfor an electrical imbalance comprises checking for an electricalimbalance between the wires.
 4. The method of claim 1 wherein monitoringsaid thermal condition comprises tracking current change to identifythermal buildup.
 5. The method of claim 1 wherein the distributionsystem comprises Power Sourcing Equipment (PSE) comprising a routeprocessor and a Powered Device comprising a line card.
 6. The method ofclaim 1 further comprising setting an alarm upon identifying said faultin one of said wires or said electrical imbalance.
 7. The method ofclaim 1 further comprising identifying a cable temperature within apercentage of a temperature limit and reducing a power level.
 8. Themethod of claim 1 wherein the PoE distribution system comprises PowerSourcing Equipment (PSE) with an output voltage between 56 volts and 58volts.
 9. The method of claim 8 further comprising detecting that theoutput voltage at the PSE exceeds 58.5 volts and shutting down theoutput voltage.
 10. A method comprising: transmitting Power overEthernet (PoE) in a PoE distribution system comprising at least twopairs of wires, at a power less than 100 watts at startup; negotiating apower level between Power Sourcing Equipment (PSE) and a Powered Device(PD) in the PoE distribution system; increasing the power to greaterthan 100 watts; periodically checking each of the wires for a fault; andchecking for an electrical imbalance at the wires.
 11. A methodcomprising: transmitting Power over Ethernet (PoE) in a PoE distributionsystem, the distribution system comprising at least two pairs of wires;periodically checking each of the wires for a fault; and checking for anelectrical imbalance at the wires; wherein periodically checking each ofthe wires comprises evaluating wire stability at least once within atime period of 10 milliseconds.
 12. The method of claim 11 furthercomprising cutting power to one of the wires for at least 0.25milliseconds and evaluating the wire and repeating for each of thewires.
 13. An apparatus comprising: a route processor operable as apower source in a Power over Ethernet (PoE) distribution system, theroute processor comprising: a plurality of ports for delivering power toa plurality of powered devices; and a fault detection module formonitoring a thermal condition in the distribution system, checkingwires at each of the ports for a fault, and checking for an electricalimbalance at the wires; wherein the fault detection module is operableto initiate a renegotiation of a power level between the power sourceand one of the powered devices upon identifying a cable temperaturewithin a percentage of a temperature limit.
 14. The apparatus of claim13 wherein checking for an electrical imbalance comprises checking foran electrical imbalance between pairs of wires and between the wires.15. An apparatus comprising: a route processor operable as a powersource in a Power over Ethernet (PoE) distribution system, the routeprocessor comprising: a plurality of ports for delivering power to aplurality of powered devices; and a fault detection module for checkingwires at each of the ports for a fault, and checking for an electricalimbalance at the wires; wherein the route processor is operable totransmit said PoE at a power less than 100 watts at startup, negotiate apower level with the powered devices, and transmit power greater than100 watts to the powered devices.
 16. A modular transport systemcomprising: a route processor comprising a plurality of ports fordelivering Power over Ethernet (PoE) at a power greater than 100 watts;a plurality of powered devices comprising a plurality of ports forreceiving the PoE; and a fault detection system for monitoring a thermalcondition in the distribution system, checking wires at each of theports for a fault, and checking for an electrical imbalance at thewires.
 17. The modular transport system of claim 16 wherein the routeprocessor comprises at least two route processors and the powereddevices comprise line cards or fabric cards.
 18. The modular transportsystem of claim 16 further comprising an extended power system forincreasing a power capacity of the route processor.
 19. A modulartransport system comprising: a route processor comprising a plurality ofports for delivering Power over Ethernet (PoE); a plurality of powereddevices comprising a plurality of ports for receiving the PoE; and afault detection system for monitoring a thermal condition in thedistribution system, checking wires at each of the ports for a fault,and checking for an electrical imbalance at the wires; wherein the faultdetection system is operable to initiate a renegotiation of a powerlevel between the route processor and one of the powered devices uponidentifying a cable temperature within a percentage of a temperaturelimit.
 20. The modular transport system of claim 19 wherein checking foran electrical imbalance comprises checking for an electrical imbalancebetween pairs of wires and between the wires.